Multiple antenna using passive reflectors



March 28, 1961 c. T. ENGBERG 2,977,464

7 MULTIPLE ANTENNA USING PASSIVE REFLECTORS Filed April 23, 1959 7 l4 ll l3 INVENTOR,

SOURCE OF CARL 7: ENGBERG. R F ENERGY I 3444,71 ail/W ATTORNEY MULTIPLE ANTENNA USING PASSIVE REFLECTORS Carl T. Engberg, Middletown Township, N.J., assignor to the United States of America as represented by the Secretary of the Army Filed Apr. 23, 1959, Ser. No. 808,541

3 Claims. (Cl. 250-) (Granted under Title 35, US. 'Code (1952), see. 266) H The invention described herein may be manufactured and used by or for the Government for governmental purposes without the payment of any royalties thereon.

The present invention relates to an antenna system using passive reflectors and particularly to a method of using a system of this type in order to insure a reliable path of communication between a transmitter and distant receiver in the face of enemy countermeasures and/or under conditions of signal fading.

A principal object of the present invention is to provide a method for obtaining reliable communications between a transmitter and receiver.

Another object of the present invention is to provide a simple and inexpensive antenna system.

A further object of the present invention is to provide a method of protecting transmitting equipment from enemy attack.

In accordance with the invention, an antenna utilizes two or more passive reflectors not quite parallel to each other, and spaced at different distances from a common radiation source, to transmit multiple beams of radiant energy from the common source but at a considerable angle relative thereto. This has the effect of concealing the true source of radiation, since the reflectors will appear to be the source or sources.

For a better understanding of the present invention, together with further objects and advantages thereof, reference is had to the following description taken in connection with the accompanying drawing in which the single figure is a diagrammatic representation of the preferred embodiment of the invention.

In the drawing is shown, as a source of radio-frequency (RF) or other radiant energy, transmitter 11 having a transmitting antenna or radiating element 12. Two passive reflectors 13, 14 are positioned to pick up energy radiating from antenna 12 and to reflect this energy in parallel paths 15, 16. In order that the reflected energy from each of the reflectors be of equal magnitude, reflector 14 furthest from the transmitting antenna 12 is of greater area than reflector 13. Additional reflectors might be used, provided those of increasing distances are of successively larger areas.

A friendly aircraft 17 may be the intended recipient of the signals from reflectors 13 and 14, for which it carries receiver 18 and antenna 19. The receiver may be otherwise situated, however. It is assumed to be located at a great distance from reflectors 13, 14 such that paths 15 and 16 are substantially parallel. This distance is very much larger than the distance between the reflectors and the transmitter, the latter distance in turn being somewhat greater than the distance between the reflectors. The reflectors may be of any suitable passive type which will efficiently reflect the radiant energy at a large angle approximating a right angle.

An enemy radiation-seeking homing missile or aircraft 21, having a direction finding set such as receiver 22 and antenna 23 would be confused by the information that it receives from the reflectors since the infor- Ere mation would appear to be coming from two apparent sources of energy. Or possibly, since the distance from one reflector to the other is relatively small, the missiles direction finding set, from a great distance, would see a fictitious source of energy between the two reflectors. As the missile approaches closer to the reflector, it would, depending on the resolving power of its antenna and its control response time either hit between the two reflectors or, at worst, probably destroy only one of them. Because the R.F. energy from the reflectors is actually generated by a single source, confusion between the reflectors is made more likely by the enemy. Since transmitting antenna 121's highly directive toward reflectors 1 3 and 14- it is unlikely that the missile could successfully home on it directly. Even if one of the reflectors is destroyed, destruction of the transmitting equipment would be prevented, and since one reflector probably would still be in operation, the communication system will not be cut off entirely.

Continued operation of the system can be insured by the use of spare reflectors at different locations, so long as care is taken that one reflector is not in the shadow of a nearer reflector. Each of the reflectors should intercept an equal solid angle of the energy beam from the directional antenna 12 if equal power is desired in each path. The reflectors may be situated in plural, alternate groups which can be switched if desired.

This communication system using plural reflectors to give spaced paths of energy radiation has several other advantages, as in tropospheric scatter systems, for example, where deep fades frequently disrupt the signal path. It is very unlikely that fades would occur in the two or more paths between the reflectors and the receiving antenna simultaneously.

The communication system described above provides for the transmission of energy from transmitter 12 to reflectors 13, 14 without the need for a power divider and transmission lines, as would be required if directional antennas were used instead of the reflectors. Further, the system has the advantage of allowing the transmitting antenna and transmitting equipment be placed in a protected location while the reflectors can be installed in rather high and exposed locations.

The foregoing disclosure relates to a preferred embodiment of the invention. Numerous modifications or alterations may be made therein Without departing from the spirit and scope of the invention as set forth in the appended claims.

What is claimed is:

1. A method of insuring a reliable path of communication between a transmitter and a distant receiver in the face of enemy countermeasures or under conditions of signal fading, said method comprising the steps of locating passive reflectors at discreet distances from the transmitter and at an angle from the direction between the transmitter to the receiver, and directing energy from the antenna of the transmitter toward the reflectors to be redirected thereby toward the receiver in substantially parallel paths.

2. A method of insuring a reliable path of communication between a transmitter and a distant receiver by preventing signal fading and at the same time protecting the transmitter from attack by an enemy, said method comprising the steps of locating a first reflector at a distance from a line between the transmitter and receiver, locating a second reflector of larger area at a greater distance from said line, adjusting the angles of said first and second reflectors so that energy from each will be directed in substantially parallel paths, directing energy from the radiating section of the transmitter toward the reflectors, and redirecting said energy by said first and second reflectors in the direction of the receiver.

3. A method of insuring a reliable path of communication between a transmitter and distant receiver by preventing signal fading and at the same time protecting the transmitter from attack by an enemy, said method comprising the steps of locating a first passive reflector at a 'distance from the antenna of the transmitter and from the line between the transmitter and the receiver, adjusting said first reflector so that a line perpendicular to its effective reflecting surface would bisect the angle between the transmitter and receiver, similarly locating a second passive reflector of larger area beyond said first passive reflector, adjusting the efiective reflecting surface of said second reflection so that it is at a slightly different angle r References Cited in the tile of this patent UNITED STATES PATENTS 2,736,894 Kock Feb. 28, 1956 2,880,310 Jakes Mar. 31, 1959 2,908,002 Van Atta Oct. 6, 1959 

